1. Field of the Invention
The present invention relates to a remote identification system carrying out data reception/transmission without physical contact between an interrogator and a transponder arranged in a relatively close distance, and more particularly to an improvement of a transponder used in the system.
2. Description of the Background Art
A remote identification system for identifying a mobile unit without physical contact via electromagnetic wave and light wave by attaching a special device to the mobile unit is showing significant progress in accordance with the drastic development of electronic technology. Such a remote identification system is used, not only in the field of manufacturing and distribution, but also in various fields such as to monitor vehicles on superhighways, and the entry/egress and the travel of people.
FIG. 6 shows a remote identification system comprising a transponder 5 attached to a mobile unit 51, and an interrogator 4 of the fixed side. Interrogator 4 comprises a transmit/receive antenna 401, a transmitter/receiver 402, and a controller 403, which are controlled by an external input/output terminal device 6. Transponder 5 has an inherent code written therein in advance. Upon receiving an interrogating signal from interrogator 4, transponder 5 modulates the received signal according to the inherent code to retransmit the same as a response signal. Interrogator 4 receives this response signal to demodulate the code to identify what the mobile unit 51 is. It is possible to rewrite the code in transponder 5 without physical contact in recent systems.
The remote identification system is given attention particularly in the field of manufacturing where the need of reduction in production time and cost by automation of the production lines are great, and where production of various products of small quantity and improvement in quality are greatly required due to the variety of consumers needs. In these manufacturing fields, transponder 5 is attached to the products transported through the production process or to palettes where the products are mounted. The mobile units are identified by reading out the data in transponder 5 at each processing step, whereby working instructions regarding the mobile units are issued to robots, automatic machines, or to the working party. The information generated at each processing step (for example, examination data) can be written into transponder 5. These data may be gathered afterwards. This will eliminate the need to access the host computer at each processing step to reduce significantly the load of the host computer. By combining the product and the information, efficient production control can be achieved.
Specific examples of a remote identification system are the bar code reader system, the system carrying out reception/transmission by light wave, and the system using electromagnetic wave of the medium frequency range. Each of these systems will be explained hereinafter.
FIG. 7 is a circuit block diagram showing a structure of a bar code reader system. The bar code reader system comprises a bar code reader 4a, a bar code 5a, and an external input/output terminal device 6. In order to read bar code 5a with bar code reader 4a, light waves from a light emitting diode (LED) or laser of a light emitting element 414 scans bar code 5a. Light wave such as of the LED is absorbed in the black portion of bar code 5a and reflected at the white portion of bar code 5a. The reflected light from bar code 5a is intensity-modulated according to the code, i.e. modulated by amplitude shift keying (ASK). This reflected light entering a photodetector 415 of bar code reader 4a causes photodetector 415 to be turned on or off according to the intensity of light, whereby the pattern of bar code 5a can be decoded by a demodulator 413. This decoded signal is sent to controller 411, where the information indicated by bar code 5a is recognized. Visible light LED, infrared LED, visible light semiconductor laser and the like can be used as light emitting element 414. Light emitting element 414 is activated by controller 411 and a light emitting element driving circuit 412.
Such a bar code reader system has the advantages of low cost and extremely thin configuration of bar code 5a, which can be used semi-permanently. Therefore, the bar code system is widely used particularly in the field of distribution.
FIG. 8 is a circuit block diagram of a structure of a remote identification system carrying out transmission/reception by light wave. The remote identification system comprises an interrogator 4b, a transponder 5b, and an external input/output terminal device 6. In order to read out data in a memory 526 of transponder 5b, a modulation signal according to the transmitted data is generated by controller 523, whereby this modulation signal is applied to an optical modulation circuit 525. In the case of transmitting a signal by ASK, light emitting element 524 emits or not emits light wave if the modulation signal is at a high potential or a low potential, respectively. This light signal is received by photodetector 425 in interrogator 4b to be demodulated to the original data by demodulator 423. The demodulated data is supplied to controller 421, where the memory contents of transponder 5b is recognized.
Conversely, in the case of the transmitting data from interrogator 4b to transponder 5b, a modulation signal according to the transmission data is generated by controller 421. This modulation signal is applied to optical modulation circuit 422. In the case the signal is transmitted by ASK, light emitting element 424 is turned on or off according to a high level or a low level of the modulation signal. This light signal is received by photodetector 521 of transponder 5b to be demodulated to the original data by demodulator 522. The demodulated data is provided to controller 523. If this received data should be stored, it is transmitted to memory 526 to be stored. Near-infrared LED is often used as light emitting elements 424 and 524.
This remote identification system utilizing optical communication has the benefits of being immune to interference of adjacent other systems due to its sharp directivity. There is also an advantage that the cost of the interrogator is low, and that data reading/rewriting is possible. Therefore, the remote identification system utilizing optical communication is often used in production lines of domestic electric equipments and office automation equipments.
FIG. 9 is a circuit block diagram showing a structure of a remote identification system utilizing electromagnetic wave of the medium frequency range. This remote identification system comprises an interrogator 4c, a transponder 5c, and an external input/output terminal device 6. Interrogator 4c reads out data stored in memory 536 of transponder 5c as follows. A carrier wave from an oscillator 432 is amplified by an amplifier 434 to be emitted as an interrogating signal from transmit antenna 435. In this case, modulator 433 just passes the carrier wave as it is. At the transponder 5c side, the interrogating signal is received by receive antenna 531 to be amplified by an amplifier 532. The amplified interrogating signal is applied to a frequency divider 535 to have the frequency thereof divided into a half, whereby the same is provided to modulator 537. Modulator 537 is also applied with a modulation signal generated by controller 534 according to data read out from memory 536. The interrogating signal frequency-divided into a half is modulated by the modulation signal and then amplified by amplifier 538. This amplified signal is re-emitted as a response signal from transmit antenna 539. At the interrogator 4c side, the response signal is received by receive antenna 436 to be amplified by an amplifier 437. The amplified signal is demodulated into the original data by demodulator 438. The demodulated data is provided to controller 431, whereby the data of transponder 5c is recognized.
In transmitting data from interrogator 4c to transponder 5c, a carrier wave from oscillator 432 is modulated by modulator 433. A modulation signal is generated by controller 431 according to the transmission data. The modulated carrier is amplified by amplifier 434 to be emitted from transmit antenna 435 as a rewrite signal. At transponder 5c side, the rewrite signal is received by receive antenna 531 to be amplified by amplifier 532. The amplified signal is demodulated into the original data by demodulator 533 to be applied to controller 534. This received data will be provided to be stored in memory 536 if required.
This remote identification system utilizing an electromagnetic wave of the medium frequency range has an advantage that data reading/rewriting is possible. There are also advantages that the communication distance is not so critical, it is not necessary to increase the attaching accuracy of the transponder since the electromagnetic wave is substantially omnidirectional, and it is hardly affected by oil stain and dirt. The remote identification system using electromagnetic wave of the medium frequency range is used in the production lines of automobiles having a relatively inferior working environment.
The bar code reader system of FIG. 7 has various disadvantages such as the bar code cannot be rewritten, the amount of data that can be included in the bar code is limited, the communication distance is short, the attaching face of the bar code is limited, the attaching accuracy of the bar code is critical, the readout of the bar code may be impossible due to oil stain, dirt and blocking objects, and the bar code itself cannot be read and understood by a person.
The remote identification system by optical communication of FIG. 8 has various disadvantages such as the attaching accuracy of the transponder becomes critical if the communication distance is long due to its sharp directivity, the lifetime of the battery of the transponder side is reduced since the conversion efficiency of light/electric is low, communication becomes impossible due to oil stain, dirt and blocking objects, and the data inside the transponder cannot be directly read out by a person.
The remote identification system utilizing electromagnetic wave of the medium frequency range of FIG. 9 has various disadvantages such as the cost of the interrogator and the transponder are high, the lifetime of the battery of the transponder becomes shorter since the transponder amplifies and transmits the response signal, the antenna must be large-sized to increase the communication distance, and the data in the transponder cannot be directly read out by a person.